In enhanced oil recovery (EOR), it is desirable to know how the flow patterns in the formation are affected by the reservoir treatment applied. Since the ultimate goal is usually to sweep the oil from the inner rock structure it is important to know if the treatment diverts the flow paths in the matrix or on the contrary increases straight channeling between an injector well and a producer well. Additionally, it would be desirable to be able to monitor the evolution of the subterranean flow paths in real time as the treatment is being carried out.
Conventional tracer materials, such as radioactive isotopes and compounds like potassium iodide, ammonium thiocyanate and dichromate, have been used to determine the origination of fluids from different injectors within a full field flood. However, such techniques often rely on breakthrough to the observation well(s) before knowledge of the fluid flow path is determined. Additionally, methods are known for evaluating fracture geometry. Some, for example employ a radioactive proppant or fracturing fluid tracers combined with gamma-ray logs. Temperature based techniques are based on the comparison of the logs made before and after the treatment with an aim of defining the regions cooled by injection of the fracturing fluid. Other fracture geometry evaluation methods include using a borehole televiewer or acoustical methods.